Field of the Invention
This invention relates to an apparatus and method for reversing well kill operations. More specifically, this invention provides a composition and method to displace killing fluids from a wellbore with naturally flowing oil or gas.
Background of the Invention
At various points in the lifetime of a well, it may be necessary to end the flow of oil, gas, and other reservoir fluids from the reservoir to the wellbore. This kind of operation is commonly referred to as a well kill. Well kills of producing wells typically involve pumping a high density kill fluid into the wellbore. The density of the kill fluid exerts sufficient pressure to prevent fluids from flowing from the reservoir into the wellbore. Kill fluids have the advantage of suppressing well production without the need for continued control from the surface.
Another advantage of using kill fluids to stop production is that such a well kill is reversible. When the well kill involves a heavy mud set in the wellbore, the reversal of the well kill requires the heavy mud to be removed. Typical removal operations involve pumping a gas into the wellbore at a high pressure. The pressure of the gas acts to remove the heavy mud from the wellbore. In some operations, the heavy mud is removed from the wellbore by being forced into the reservoir. This method is cheap, but runs the risk of causing damage to the reservoir. In an alternate method, coiled tubing is inserted into the wellbore. The high pressure gas is inserted through the coiled tubing, circulates out the bottom of the coiled tubing, and lifts the heavy mud up out of the wellbore. The coiled tubing method does not run the same risk to the reservoir, but requires more equipment making it a more expensive reversal option.
A well kill with injected gas is advantageous, because the injection gas is usually a cheap, inert gas such as nitrogen. The injected gases themselves do not prevent the flow of reservoir fluids into the wellbore allowing production to begin promptly upon removal of the kill fluid.
A method with the advantages of injected gas and the minimized risk to the reservoir of coiled tubing and without the operating costs of coiled tubing would be preferred.